The brain is the control centre for every activity of the body, conscious as well as involuntary actions. It is suspended in clear (cerebrospinal) fluid and surrounded by the skull (cranium) for its protection.

There are three types of receptor or sense organs depending on where they are found.

Exteroceptors receive information from outside the body. Examples of these are the eyes, ears and skin.

Interoceptors receive information from organs inside the body including the lungs and digestive system.

Proprioceptors are found mainly in the muscles, tendons and joints. They respond to the degree of stretching in their particular body part and so give information about relative positions of different parts of the body. Proprioceptors enable us to move our limbs with great accuracy and speed without the need to actually watch them.